zeroed tensor at end of Flatten #838

Job	Run time
sdist	2m 41s
format_clang	15s
bld (linux_release_64, ubuntu-20.04, -release_64, -asm)	2m 44s
format_ruff	6s
bld (linux_debug_64, ubuntu-20.04, -debug_64)	2m 44s
vis	2m 41s
bld (mac_release_64, macos-13, -release_64, -asm)	1m 56s
bld (mac_debug_64, macos-13, -debug_64)	1m 14s
bld (mac_release_arm, macos-14, -release_arm, -asm)	42s
bld (mac_debug_arm, macos-14, -debug_arm)	27s
bld (win_release_64, windows-2022, -release_64)	1m 35s
bld (win_debug_64, windows-2022, -debug_64)	1m 5s
testS	1s
docs	1s
testC	1s
bdist	1s
testB	1s
npm	1s
R	1s
powerlift	1s
test_powerlift	1s
testR	1s
	18m 20s

Provide feedback